Fix create url encoding

I'm not sure on the intended functionality here but it seems to be broken to me.

running:

`$this->createUrl('checkout/confirmation', array('order'=> array('666', '999')));`

Gives me:

`/checkout/confirmation/order%5B0%5D/666/order%5B1%5D/999/`

Again I'm not sure if the encoded square braces were intended, although I can't see why they would be.

This fix just changes the way the encoding is applied on the array keys in a parameter.

Thanks